Adriëtte Oostvogels

38 Chapter 2 BP course during pregnancy BP was measured at each prenatal visit by the obstetric caregiver (midwife/ obstetrician). Blood pressure measurements were done in a seated position using the appropriate cuff size, mostly measured on the right arm. More than 85% of the obstetric caregivers used an auscultatory device to measure blood pressure (using Korotkoff phase I for systolic BP (SBP) and Korotkoff phase V for diastolic BP (DBP)), while the remainder of the obstetrics caregivers used an automated BP monitor. BP and date of measurement were retrieved from obstetric medical files. A mean of 10 (SD=2.3) BP measurements per pregnant woman were obtained. On average the first measurement was at 12.9 (SD=2.0) weeks of gestation and the last at 38 (SD=3.4) weeks. When medical files stated the use of anti-hypertensive drugs (n=25) from a certain date onwards [mean gestational age (SD)=33.6 (3.6) weeks], BP measurements after that date were excluded. Double entry was performed in a randomly selected sample of 315 (5%) records. Agreement on overall BP was high for SBP (97.8%) and DBP (97.2%). Covariates Covariates were chosen a priori based on their association with maternal weight status or BP. 5,7 Chosen covariates included maternal age (years; continuous), education (years after primary school; continuous); parity (nulliparous/multiparous), ethnicity [Dutch, Surinamese-Hindu, Caribbean (Surinamese-Creole/Antillean/Aruban), Turkish, Moroccan, Ghanaian, other], and smoking and alcohol use during pregnancy (yes/no) which were self-reported in the pregnancy questionnaire. Ethnicity was based on the country of birth of the pregnant woman’s mother. Gestational age at blood sampling, gestational age at giving birth (days) and foetal sex (male/female) were obtained from the Youth Health Care Registration. Gestational age was based on ultrasound or, when not available (±10%), was calculated by the obstetric care provider, based on the first day of the last menstrual period. Gestational age at blood sampling was calculated based on gestational age at birth, date of birth and date of blood sampling. Statistical analysis Descriptive statistics of the study population, comparing women with normal weight and overweight, and the non-response analysis, comparing women in this study with women without either an early pregnancy lipid profile or BP course during pregnancy, were performed using independent samples t-tests for continuous variables and χ 2- tests for categorical variables. To reclaim the cases with missing values, multivariate